This invention relates to a nuclear fuel element containing nuclear fuel therein for use in a nuclear reactor.
A nuclear fuel element for use in a nuclear reactor comprises an elongated tube formed of heat-resistant alloy such as stainless steel, nuclear fuel pellets contained in the tube, and a setting structure for immovably positioning and setting the pellets in the axial direction of the tube. In the nuclear fuel element, nuclear fission of the fuel caused by irradiation of neutron or the like accompanies FP-gas (nuclear fission product) generation, so that it is necessary to elongate the tube far longer than the total length of the tube occupied by the fuel pellets to provide enough space for receiving FP-gas therein at lower pressure.
Therefore, a conventional nuclear fuel element has, as shown in FIG. 1A, a tube 1, a lower end plug 2 securely fixed to an end of the tube 1, fuel pellets 3 located at the lower end plug side of the tube, an upper end plug 6 securely fixed to the other end of the tube 1, a sleeve 5 placed adjacent to the upper end plug 6 in the tube, and a spring 4 inserted between the pellets and the sleeve to immovably set the pellets 3. Another nuclear fuel element is shown in FIG. 1B in which the fuel pellets 3 are set by an elastic stopper 7 through spring 4, the elastic stopper 7 being forced into the tube 1 and the fuel middle of the tube 1 due to functional engagement with the tube inner wall.
The FIG. 1A embodiment is disadvantageous in that the elastic force of spring 4 is applied by way of sleeve 5 to the upper end plug 6 so that the aerial space for receiving FP-gas in the tube becomes less because of the sizable space occupied by the sleeve 5. The FIG. 1B embodiment is disadvantageous in that elastic stopper 7 is in danger of moving and injuring the tube on shock or acceleration during transportation of the tube.